Net Income per Share - Computation of Basic and Diluted Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income	$ 21,390	$ 12,713	$ 53,033	$ 29,786
Less: Net income allocated to unvested participating restricted stock	(719)	(428)	(1,827)	(1,000)
Net income available to common stockholders - basic	20,671	12,285	51,206	28,786
Dilutive Securities, Effect on Basic Earnings Per Share, Options and Restrictive Stock Units	7	0	20	3
Net income available to common stockholders - diluted	$ 20,678	$ 12,285	$ 51,226	$ 28,789
Weighted average outstanding shares of common stock - basic (in shares)	17,181	17,544	17,262	17,623
Dilutive effect of stock options (in shares)	382	259	364	204
Weighted average outstanding shares of common stock - diluted (in shares)	17,563	17,803	17,626	17,827
Net income per common share - basic (USD per share)	$ 1.20	$ 0.70	$ 2.97	$ 1.63
Net income per common share - diluted (USD per share)	$ 1.18	$ 0.69	$ 2.91	$ 1.61